The overall objective of this project is to characterize and elucidate the immunopathogenesis of type I insulin-dependent diabetes melitus (IDDM). These studies will test the hypothesis that cellular and/or humoral immune mechanisms may play a role in the etio-pathogenesis of IDDM. This will be done by developing, perfecting, and employing a variety of assays measuring and monitoring immunological relations to pancreatic islet cells in vitro, in human subjects with IDDM, and their relatives, and also in the BB rat model for IDDM. In human subjects, islet cell cytotoxic antibodies (C'AMC) will be measured in the serum of subjects with recently-diagnosed IDDM, and their first-degree relatives, to determine if C'AMC may be predictive of reduced islet B cell insulin secretory capacity. New immunological assays will be developed to detect islet-specific lymphoproliferative and cytotoxic effects of peripheral blood mononuclear cells (PBMC) from human subjects with IDDM. PBMC (T-lymphocytes, B-lymphocytes, monocytes, NK cells) in recent-onset IDDM subjects and their first-degree relatives will be phenotyped, using a panel of monoclonal antibodies and flow cytometry to determine which markers might be useful to monitor disease activity. The effects of immunotherapy with cyclosporine on the above immune parameters will be determined in subjects with recent-onset IDDM to determine if any of these parameters monitor the relevant anti-islet immunologic response(s). Islet-specific lymphoproliferative and cytotoxic cellular immune responses will be measured also in BB diabetic rats to determine if these responses are related to the presence and severity of diabetes. Islet-specific cytotoxic lymphocytes (CTL) detected in diabetic BB rats will be cloned and those clones specifically cytotoxic for islet B cells will be identified and expanded. Our experience in islet B cell purification will be used to obtain homogeneous populations of islet B cells to confirm that the above-described islet-specific immune reactions are islet B-cell directed. The ability of islet-specific CTL to precipitate diabetes will be tested in prediabetic and diabetes-resistant BB rats, and normal MHC-compatible (Wistar Furth) rats.